PAK1 inhibition with Romidepsin attenuates H-reflex hyperexcitability after spinal cord injury

Hyperreflexia associated with spasticity is a prevalent neurological condition characterized by excessive and exaggerated reflex responses to stimuli. Hyperreflexia can be caused by several diseases including multiple sclerosis, stroke and spinal cord injury (SCI). Although we have previously identified the contribution of the RAC1-PAK1 pathway underlying spinal hyperreflexia with SCI-induced spasticity, a feasible druggable target has not been validated. To assess the utility of targeting PAK1 to attenuate H-reflex hyperexcitability, we administered Romidepsin, a clinically available PAK1 inhibitor, in Thy1-YFP reporter mice. We performed longitudinal EMG studies with a study design that allowed us to assess pathological H-reflex changes and drug intervention effects over time, before and after contusive SCI. As expected, our results show a significant loss of rate-dependent depression - an indication of hyperreflexia and spasticity - 1 month following SCI as compared with baseline, uninjured controls (or before injury). Romidepsin treatment reduced signs of hyperreflexia in comparison with control cohorts and in pre- and post-drug intervention in SCI animals. Neuroanatomical study further confirmed drug response, as romidepsin treatment also reduced the presence of SCI-induced dendritic spine dysgenesis on alpha-motor neurons. Taken together, our findings extend previous work demonstrating the utility of targeting PAK1 activity in SCI-induced spasticity and support the novel use of romidepsin as an effective tool for managing spasticity.